The present invention relates to apparatus for detecting the condition of two switches connected to a single transmission line.
Many systems are electronically controlled using microprocessors which are supplied with signals from external sensors. In many systems, the sensors comprise switch devices of one sort or another and it is important to be able to recognise the condition of each switch device. Ideally, each switch device would be connected to the microprocessor by a respective transmission line or else a bus would interconnect all switch devices and each switch device would have a unique address. The first of the ideal solutions is not possible in some circumstances due to lack of space and the second is expensive and requires a special construction of control system. There thus occurs in practice a situation where more than one switch device is connected to a processor by a single transmission line.
It is possible to evaluate the conditions of two switch devices on a single transmission using digital evaluation techniques in a digital channel, but often all digital channels in a microprocessor are fully utilised.
The present invention provides an arrangement whereby an analog channel can be used to evaluate the condition of each of two switches on a single analog transmission line.
The advantages of this arrangement are that no analog channel into the processor is required and hence no A/D conversion. Processor inputs designed for other tasks can be utilised with a resulting in saving of development time and cost.